
let stu = {
    id: 1002,
    name: '马飞燕',
    age: 20 ,
    married: undefined
}

console.log( 'married: ' , stu.married , ' has: ' , stu.hasOwnProperty( 'married' ) );
console.log( 'gender: ' , stu.gender , ' has: ' , stu.hasOwnProperty( 'gender' ) );